From all the currently known mycotoxins, aflatoxin B1 (AFB1) presents the greatest public health and agro-economic significance. Its metabolite, aflatoxin M1 (AFM1) has toxicological properties comparable to those of AFB1, albeit a lower carcinogenic potency.The occurrence of AFM1 in milk marketed in Portugal and the evaluation of the exposure degree to the toxin through its consumption in an average citizen were studied. Estimation of the corresponding concentration of AFB1 in feedstuffs was also aimed.Forty samples representing the totality of the pasteurized and UHT half-skimmed milk brands marketed in the country were surveyed. Determination of AFM1 was carried out by means of a commercial competitive ELISA.Eleven samples (27.5%) featured a contamination above the detection limit (mean 23.4 ± 24.0 ng/L). Two milk samples (5%) both produced in Azores presented AFM1 values that surpassed the legal maximum limit (50 ng/L). A third sample, also from the Azores Islands, presented a very high value of contamination. These results are interesting given that dairy production in Azores is traditionally pasture-based which is considered as low risk system regarding AFs contamination.Adult average dietary exposure to the fungal toxin through milk consumption was estimated at 0.08 ng/kg bw/day, which is inevitably higher for infants, considered the main risk group. The concentration of AFB1 in the feeds consumed by the producing cows was estimated as 1.46 μg/kg.The results call for further studies in an attempt to identify and thus control potential influencing factors in the only region where milk samples contaminated above the legal limit were produced.